Over a period of years,
builds up in a car's
is left in all year round.
Eventually the sediment will start to obstruct the water passages in the
. Such obstruction causes overheating of the
which, if it becomes severe, can lead to engine seizure.
If your engine is overheating and you have eliminated other possible causes, such as leaks (See
Adjusting the static timing
), the water passages are probably choked or narrowed by sediment. To clear them, thoroughly flush the radiator and engine.
Before flushing, drain the old
from the system and discard it the sediment deposits will have contaminated it. Remember, however, that the antifreeze contained in the coolant is poisonous. Have a large container ready to collect it, for disposal later at your nearest dump for poisonous wastes.
With the engine cold, remove the
from the radiator or
. Turn the heater control to
If the radiator has a drain plug, remove it; if there is a drain tap, open it - look in your car handbook to see which way it turns, as it can be broken easily.
If no coolant runs out, gently poke the hole clean with a piece of wire, or unscrew the tap completely.
If there is no tap or drain plug, disconnect the bottom
at the radiator end.
There may also be a drain tap on the
. If so, open it.
How to flush a car radiator
Disconnect both hoses from the radiator. Push the end of a garden hose into the top radiator connection stub, and
it with rags.
Refit the radiator
cap and turn the water on full. Flush until the water runs clear.
Check by catching some water in a glass jar and looking for sediment which you can see only in still water.
If the water does not clear in a few minutes,
the radiator. Seal the hose into the bottom stub. Tie a long plastic bag with a hole in the bottom to the top stub, to direct the coolant away from the engine and electrical components. Flush until the water runs clear.
Flushing the engine block
Disconnect the top hose from its stub on the
housing above the
Unbolt the top of the housing and lift out the thermostat, noting which way up it
. Refix the top of the empty housing.
Seal a garden hose into the housing stub. Flush until water runs clear from the bottom hose. This is reverse flushing: water normally flows up the engine.
Refit the radiator if you removed it, and put back the thermostat. Fit a new
in the thermostat housing, after smearing both sides of it with non-setting
. Bolt back the top.
Reconnect the hoses, renewing any damaged hoses or clips or any that are more than four years old.
Refill the system with clean water. Run the engine up to its normal working temperature and check for leaks.
Almost all car engines work on the four-stroke cycle, so called because it
takes four strokes of the piston induction, compression, ignition and exhaust -
to produce one firing of the fuel/air mixture. This means that the crankshaft
rotates twice to complete each cycle.